1. Field of the Invention
The present disclosure relates to a nitride semiconductor device and a method for producing the same.
2. Description of Related Art
A conventional process for producing nitride semiconductor devices involves forming a buffer layer made of a nitride, such as AlN, which moderates lattice constant mismatch, on a sapphire substrate or the like, and further stacking a gallium nitride-based semiconductor by metalorganic chemical vapor deposition. Japanese Patent Application Publication No. 2006-080378 and Japanese Patent Application Publication No. 2013-065849, for example, each discloses a process for stacking, as buffer layers, a first buffer layer made of high carbon concentration AlN and a second buffer layer made of low carbon concentration AlN, and further stacking a defect-reducing layer made of undoped GaN for reducing crystal defects by metalorganic chemical vapor deposition. Japanese Patent Application Publication No. 2009-081406 discloses a process for forming a buffer layer made of AlN on a sapphire substrate by sputtering, and further stacking an undoped GaN layer as an underlayer by metalorganic chemical vapor deposition.